Process of oxidizing lead.



lil

alkali metal as a catalytic or facilitating re- ITE if CLIFFORD 1D.HOLLEY, 0F DETROIT, IVIICHIGAN, ASSIGNOIR T0 ACIlWIE 'VTIt-II""lLl lll'ljl ill-BL ND COLOR WORKSQ O]? DETROIT, ltIIGI-IIGAN, L l,UCJlEtEUItJ-Mtlltlll 01F l llilll.

specification 0t No Drawing".

letters Patent.

Application filed ll'ebrnary ill, will.

. tri l, Ti l llllIthlll'l'lEl llfiill'll'l.

To all whom it may concern.

Be it known that l, CLIFFORD D. Hotter, a citizen of the United States,residing" at Detroit, in the county of ll ayne and State of Michigan,have invented certain new and useful Improvements in Processes ofOXldlI/r ing Lead, of which the following is a'speci fication.

This invention relates to processes of oxidizing lead; and it comprisesa method of oxidizing metallic lead wherein finely-dividcd lead isoxidized. by air in the presence of a solution containing the nitrate ofan agent, such nitrate bein, ordinarily subse quently regained as analkali, nitrite: such solution being; advantageously a waste liquorderived from the manufacture of lead chrtr mate and containing an alkalinitrate, such as sodium nitrate, as well as, usually, free nitric acid;all as more fully hereinafter set forth and as claimed.

When submerged in or wet with Watr, l'iright surfaces of metallic leadare oxidized by air, if air has access to the liquid, with theproduction of a. hydrated oxid of lead of basic and reactive properties.With Water alone he reaction never goes very far, neither is it veryrapid. even in attrition 'irocesses where the lead oxid formed is keptscoured oil by attrition. With Water containing saline "or otherionizable sub stances, such as acids, and particularly where theseacids, as isthe ease with nitric and acetic acids. form solubleleadsalts, the action is facilitated, partly. probably, at first by remoralof the oiiid from the affected surfaces in the case of the acids andpartly, probably. for more obscure reasons connected with the presenceof ions. lioth acetic and nitric acids have been proposed for use insuch processes. The former is, directly or indirectly, the corrodingagent in the Well known Dutch process, which, while yielding a. highgradepinmcnt, is relatively very slow and expensive. The use of nitricacid in proposed 'n-ocesses of making lead oxid has, as a rule, not beensuccessful in practice. in -1n y copending application Serial No.588,973, filed October 2'5, 1910, l have, however, disclosed acommercially practi :able method of making oxids of lead in which nitricacid is employed. ln the aforesaid application I have also disclosed,but have not claiined specifically, a niodiiied process in whichnitrates such as sodium nitrate and the like, either alone or inconnection with nitric acid, malt take the place of nitric acid per so.The present application is in part, therefore, a continuation of myprior application aforesaid. ll hcre nitric acid alone is employed it isapt to undergo a far-going reduction, lirst forming lead nitrates andthen nitrites with, ulti mately, formation of neutral nitrogen oxide andammonia. ilcids of course do not lone; remain as such in the presence ofthe lead undergoing oxidation, but become col'iverted into laid salts byreaction with the lead oxid produced.

1 have discovered that, for some purposes a much better facilitating orcatalytic agent is to be found in solutions of the nitrates of theallcalis, such as nitrate of sodium or nitrate of potassium, the formerbeing the better. Nitrates of alkaline earths, such as nitrate ofcalcium, barium, strontium and magnesium are less suitable and do notyield commercially valuable by-prmluc llnlilre the nitrate of lead, thealkali nitrates do not undergo a far-reaching reduction but arecrmvertedinto nitrites from which in the course of the operation nitrates areprob ably regei'ierated by the action of the air; these nitrates thusacting); as carrier a cents.

Whatever may be the chemical mccliiihisin of the reactions involved, lhave found that a solution of an alkali nitrate. and particu' larly asolution of sodium nitrate, acts an ei'iern'ctic oxidizing agent in thecorrosion of lead in the presence of water and air, auichening'tlwoperation very imaterially and givii'ig a desirable type of hydra. ba'cand reactive otid of lead from ah white lead, in: ico't, litlnlrgi-l,niiniuni other pitnnentary load product quality may be made. its is wellpigmentaly value of oxid ed, leaf :irod: depends very much on theirmole." l stitution; it being practically im ossible, for example, tomake a ,e'ood red lead, or, in fact, cmnn'iercially, any red lead, fromsome forms of lead odd, as for example, from. fused litharge. 'ihchydrated or made under the present inn-anion is re active andmolecularly line and. with proper methods of treatment. carries itsreactivity and fineness of constitution throughout in.

conversion into other anc pigmentary lead products; giving, for example,a tinegrained dawn, the t till lltl

all

l Oil white lead of good covering power, a fine high grade minium or redlead of unusual volume for its Weight, etc.

After the oxidation of lead in the presence of a solution of an alkalinitrate, the

latter is converted into and remains in such solution as an alkalinitrite; sodium nitrate, for example, becoming sodium nitrite, acommercially valuable product useful for many purposes, as in the dyeand color industries. This nitrite may be regained, as by. evaporationof the residual solution from the oxidation and utilized.

A cheap and particularly suitable nitrate solution for the presentpurposes is found in the waste liquor from the manufacture of leadchromate; a liquid which is ordinarily sent to the sewer and which ishereinafter termed chromate waste liquor. Lead chromate is ordinarilymade by double de composition between a solution of lead nitrate and asolution of an alkali bichromate or chromate. Ordinarily sodiumbichromate or chreinate is employed; more rarely, the potassium salt isused. Chromate of lead is formedand precipitated by a well-knownreaction and nitric acid and alkali nitrate remain in. the solution.With a bichromate, half the nitric acid is free and half is in acombined form. There sodium bichromate and lead nitrate are used as isusually the case, for each molecule of lead chromate formed thereremains in the residual solution a molecule of sodium nitrate and amolecule of free nitric acid. This residual solution, or chromate wasteliquor, I find particularly suitable for my purposes since it exercisesa very vigorous action upon finely divided lead in the presence ofairand forms a desirable type of hydrated or basic reactive leadoxid.While solutions for my purpose may be formed by direct solution or"commercial nitrate of soda in Water, I prefer this'chromate waste liquornot only on account of its cheapness but because or" its advantages inpractical work.

It seems to be rather more reactive than a directly produced nitratesolution.

The free nitric acid in the waste liquor may be preliminarilyneutralized by soda or soda ash to convert it into sodium nitrate; butthis is not ordinarily necessary. If not so neutralized however itundergoes farreaching reduction in the process, even so far as ammonia,and is, or may be, ultimately not recovered as a useful product as isthe case where it is converted into sodium nitrate which may berecovered later as sodium nitrite. The presence of free nitric acid inthe liquor to begin with'is however often advantageousv in my processfor the reason that with some varieties or" comminuted lead carryingoxidized coating layers it exercises af solyent action on the oxid inthe beginnlngof the operation upon a charge of lead, much acceleratingthe progress of the oxidizing action.

Any of the ordinary finely divided forms of lead, such as moss lead,dust lead, blue lead and the like, may be employed. Blue fume is not sosuitable since it contains lead sulfate and sulfid. Lead shavings andchips are likewise not so well adapted being too coarse. In the presentprocess, the lead should be in a state of quite fine subdivision. Anyapparatus adapted to give a good aeration of lead in the presence ofliquid may be employed in my process, such as rotating drums and theother apparatus often employed for oxidizing lead by wet processes.lt'is not necessary to use high heats or any heat beyond atmospheric andit is also on: necessary to use artificial cooling.

should be such as to give eiiicient aeration since in the presentprocess the oxygen of the air is relied upon for the major part or" theoxidation, the nitrate acting largely as a facilitating reagent.

Any strength of nitrate solution between two per cent. and 50 per cent.may be em ployed. A solution containing as little as two per cent. isefficient as a catalyzing agent; but with stronger solutions where thesodium nitrite is to be subsequently recovered the operation is cheaperas involving less expense in such recovery. The relative amount ofliquid may vary from enough to cover the lead and form a body of iquidto merely enough to convert the lead into a.

the present invention, and where such recovery is efiected of course theuse of strong solutions of nitrate producing final strong solutions ofnitrite is desirable. While potassium nitrate, or waste chromatc liquorcontaining potassium nitrate, may be employed in this invention itoffers no advantage over sodium nitrate, or waste chromate liquorcontaining sodium nitrate; and I re gard sodium nitrate, for manyreasons, as in any event being rather better adapted for my purposes.

In a practical embodiment of the described prccess, I may place 4000pounds of dust lead in a drum'with 460 gallons of waste chroma teliquor, containing, say, 8 per-"cent. bfsodium nitrate and 4 per cent.of free nitriacid and agitate with free ac cess of air for 24: to 48hours. The lead is thereby converted. into a reddish orange hydratedreactive basic oXid of large bull:

for its Weight while the nitric acid of the original solution disappearsand the sodium nitrate is converted into an equivalent amount of sodiumnitrite. The oxid may be separated from theresidual liquid by anyconvenient means, such as subsidence and pressing and washing, and maybe marketed as it is, or, and usefully, it may be converted intopigmentary products for which its state of subdivision and molecularconstitution render it particularly well adapted. By a gentle heating itmay be dehydrated and converted into massicot of exceptional quality,while a continuation of the heating under oxidizing conditions convertsit into an extremely high grade red lead. By modifying the heatingcond|t1ons it may, of course, be converted into a very fine-grainedlitharge. The hydrated oxid may be gassed with carbon dioxid to convertit into white lead. The chromate 'aste liquor may, or may not, beneutralized with sodium carbonate or bicarbonate preliminarily. If soneutralized the quantity of sodium nitrite to be recovered is increasedand some advantages are gained in the operation. The liquor from whichthe hydrated oxid is separated may be simply evaporated to regain sodiumnitrite.

The preliminary separation of the residual liquor may be omittedwherered lead is to be made, the material being dried and fur naced toproduce red lead. The presence of the nitrite facilitates the oxidationto red lead and'after the red lead is formed, the nitrite may then beleached out and regained. In this modification of my invention, in thefinishing stages of the first er aerial oxidation the water of thesolution may be allowed to evaporate and pass away with the air to alarge extent as reducing the cost of the subsequent "drying prior to thered lead oxidation.

Where the nitrite'solution is separated from the hydrated oxidpreliminarily to drying and re-oxidation to red lead, if the hydratedoxid be not washed too thoroughly" enough nitrite will remain in it toaid materially in such reoxidation. \Vhile alkali nitrites do not appearto he changed or destroyed to any extent inthe oxidation of leadprotoxid to minium or red lead their presence gives a smoother andquicker oxidation with the production of a better article. With smallamounts of nitrite, say from one per cent. down, it need not be removedfrom the finished red lead. A quarter per cent. of nitrite is sufiicientto aid materially in making red lead.

In a typical embodiment of my process in making red lead, finely dividedlead may be oxidized by air in the presence of sodium nitrate solution,or Waste chromatc liquor in the manner previously described and aftercompletion of the reaction the lead oxid may be separated from the. bulkof the solution by subsidence and draining and then dried withoutwashing. The drled material may then be furnaced under oxidizingconditions at a low temperature to convert it into red lead and thendirectly marketed Without leaching.

I claim:

1. The process of oxidizin lead which comprises exposing'finely divi edlead to the simultaneous action of a solution of an alkali nitrate andof air.

2. The process of oxidizin lead which comprises exposing finely divi edlead to the simultaneous action of a solution of an alkali nitrate andof air, to obtain a mass comprising oxidized lead and alkali nitrite.

3. The process of oxidizing lead which comprises exposing finely dividedlead to the simultaneous action of a solution of sodium nitrate and ofair.

4. The process of oxidizing lead which comprises exposing finely dividedlead to the simultaneous action of chromate waste liquor containingalkali nitrate and of air.

The process of oxidizing lead which comprises exposing finely dividedlead to the simultaneous action of chromate waste liquor containingsodium nitrate and of air, and.

thereafter separating oxidized lead and sodium nitrite.

6. The process of oxidizin lead which comprises exposing finely divi edlead to the simultaneous action of neutralized chromate waste liquorcontaining alkali nitrateand of.

air.

7 The process of oxidizin comprises exposing finely divii ed lead to thesimultaneous action of neutralized chromate waste liquor containingsodium nitrate'and of air. and thereafter separating sodium nitrite andoxidized lead.

8. The process of making lead oxid which comprises exposing finelydivided lead to the simultaneous action .of air and alkali nitratesolution, recovering the lead oxid, and then converting such oxid intored lead by heat and oxidation.

9. The process of making lead oxid which comprises exposing finelydivided lead to the .nmltaneous action of air and sodium nitratesolution, recovering the lead oxid, and then converting such oxid intored lead by heat and oxidation.

in testimony whereof, I aiiix my signature in the presence of witnesses.

(ULlFl ORl) l). LHOLLEY.

\Vitncsses:

N. J. Susan, H. E. Crank.

